1. Field of the Invention
The invention relates to determination of the relative difference in capacity between two capacitors and, more particularly, to angular measurement with respect to gravity using a capacitive sensor.
2. Description of the Prior Art
Prior art designs of capacitive sensors used to provide an angular measurement with respect to gravity consist of utilizing the capacitive elements in bridge circuits excited by a high frequency oscillator. Changes in capacitance due to tilt unbalance cause the bridge circuit to provide a change in the output frequency or a change in the output voltage level. An apparatus of the foregoing type is described in U.S. Pat. No. 4,442,243, issued Dec. 27, 1983. Another prior art device incorporates a force feedback accelerometer wherein a mass is suspended between electromagnets. As the assembly is tilted, the mass moves. Power is applied to the magnets to recenter the mass. The current required to recenter the mass is converted to a measure of angular displacement. The present invention uses the capacities of a capacitive sensor at a tilt angle to establish two pulses of different widths, provides circuitry to determine the relative pulse widths and supplies a signal, derived from the relative pulse widths, that is representative of the tilt angle.